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K >>1 Forward rxn dominates (rxn lies to

K >>1 Forward rxn dominates (rxn lies to the right). Mostly products at equilibrium, [products] >> [reactants]. K <<1 Reverse rxn dominates (rxn lies to the left). Mostly reactants at equilibrium, [products] << [reactants].

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K >>1 Forward rxn dominates (rxn lies to

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  1. K >>1 Forward rxn dominates (rxn lies to the right). Mostly products at equilibrium, [products] >> [reactants]

  2. K <<1 Reverse rxn dominates (rxn lies to the left). Mostly reactants at equilibrium, [products] << [reactants]

  3. K  1 Forward and reverse rxn occur to roughly the same extent, [products]  [reactants]

  4. 2.0 moles of NH3 gas are introduced into a previously evacuated 1.0 L container. At a certain temperature the NH3 partially dissociates by the following equation. At equilibrium 1.0 mol of NH3 remains. Calculate the equilibrium constant for this reaction.

  5. Reaction Quotient (Q) Q = K: The rxn is at equilibrium. No shift. Q < K: The rxn shifts right to produce products to increase Q. Q > K: The rxn shifts left to produce reactants to decrease Q.

  6. Le Chatelier’s Principle If a change (stress) is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change (stress).

  7. Le Chatelier’s Principle • SO2(g) is removed. • O2(g) is added. • SO3(g) is added. • The volume of the reaction container is halved. • An inert gas like Ar is added. • A catalyst is added. • Temperature is increased.

  8. Le Chatelier’s Principle • CO2(g) is added. • CaCO3(s) is added. • The volume is increased. • The temperature is decreased.

  9. 1.0 mol of N2O4(g) is placed in a 10.0 L vessel and then reacts to reach equilibrium. Calculate the equilibrium concentrations of N2O4 and NO2. K = 4.0 x 10-7

  10. Brønsted-Lowry Model Acids – are proton donors Bases – are proton acceptors

  11. HC2H3O2 is a stronger acid then HCN which Has the stronger conjugate base?

  12. Comments on the Conjugates of Acids and Bases. • The weaker the acid the stronger its conjugate base. • The weaker the base the stronger its conjugate acid. • The conjugate base of a weak acid is a WEAK base. • The conjugate base of a strong acid is worthless. • The conjugate acid of a weak base is a WEAK acid.

  13. Stuff you should now know. • Ka value is directly related to acid strength. • Weak acids vs. strong acids (Ka’s and % dissociation. • Conjugate acid-base pairs. • KaKb=Kw • Kb value is directly related to base strength. • How to write out Ka and Kb rxns and expressions. • The weaker the acid the stronger the conjugate base (and vice versa). • Conjugate bases of strong acids have no basic properties whatsoever! (Kb << Kw)

  14. Calculate the pH of a 0.10 M HBr solution.

  15. Calculate the pH of a 0.10 M HOCl solution. KaHOCl = 3.5 x 10-8

  16. Calculate the pH of a 0.10 M NaF. KaHF = 7.2 x 10-4

  17. Calculate the pH of a 0.10 M Ca(OH)2 solution.

  18. Calculate the pH of a solution containing 0.10 M HOCl and 0.02 M NaOCl. KaHOCl = 3.5 x 10-8

  19. Calculate the pOH of 0.05 M Ba(OH)2.

  20. Calculate the pOH of 0.50 M KOCl. KaHOCl = 3.5 x 10-8

  21. Calculate the pOH of 1.00 M HI.

  22. Calculate the pOH of 0.25 M NH4Cl. Ka NH4+ = 5.6 x 10-10

  23. Calculate the pOH of a solution containing 0.25 M NH4Cl and 0.10 M NH3. Ka NH4+ = 5.6 x 10-10

  24. Calculate the pH of 1.6 x 10-13 M HNO3.

  25. A solution of 8.00 M HCOOH is 0.47% Ionized. What is the Ka for the acid? pH?

  26. AcidKa HF 7.2 x 10-4 C6H5NH3+ 2.6 x 10-5 HC2H3O21.8 x 10-5 HCN 6.2 x 10-10 NH4+

  27. Acidic, Basic, or Neutral? • NaCN • NH4NO3 • KI • LiC2H3O2 • C6H5NH3Cl • KF • NaNO3 • HClO4 • Ca(OH)2 • NH4CN • NH4C2H3O • CaO • SO3

  28. Acidic, Basic, or Neutral? • NaCN Na+ - worthless, CN- - weak base, basic • NH4NO3 NO3- - worthless, NH4+ - weak acid, acidic • KI K+ - worthless, I- - worthless, neutral • LiC2H3O2 Li+ - worthless, C2H3O2- - weak base, basic • C6H5NH3Cl Cl- - worthless, C6H5NH3+ - weak acid, acidic • KF K+ - worthless, F- - weak base, basic • NaNO3 Na+ - worthless, NO3- - worthless, neutral • HClO4 HClO4 – strong acid, acidic • Ca(OH)2 Ca(OH)2 – strong base, basic • NH4CN KaNH4< KbCN-- basic • NH4C2H3O KaNH4 = KbC2H3O- - neutral • CaO metal oxide - basic • SO3 nonmetal oxide - acidic

  29. Buffers Buffer – A solution where a weak acid and its conjugate base are both present in solution. • Buffers resist changes in pH

  30. Good Buffers • Good buffers will have the following: • EQUAL concentrations of the weak acid and its conjugate base. • LARGE concentrations of the weak acid and its conjugate base. • pKa = pH of desired pH.

  31. Examples of Buffers • HCN/CN- • NH4+/NH3 • H2PO4-/HPO42- - intracellular fluid buffer • H2CO3/HCO3- - blood buffer

  32. Calculate the pH of a solution that is 1.00 M HNO2 and 1.00 M NaNO2. KaHNO2 = 4.0 x 10-4

  33. Calculate the pH when 0.10 mol of HCl is Added to a 1.00 L solution containing 1.00 M HNO2 and 1.00 M NaNO2. KaHNO2 = 4.0 x 10-4

  34. Calculate the pH when 0.10 mol of NaOH are added to a 1.0 L solution containing 1.00 M HNO2 and 1.00 M NaNO2. KaHNO2 = 4.0 x 10-4

  35. Calculate the pH of a solution formed by Mixing 500.0 mL of 0.100 M NH3 and 500.0 mL of 0.0500 M HCl. KbNH3 = 1.8 x 10-5

  36. You want to prepare a HOCl buffer of pH 8.00. You want to make a 500. mL solution and use all of the 0.75 mol of HOCl you have on hand. How many mol of KOCl must you add? KaHOCl = 3.5 x 10-8

  37. Calculate the pH of a solution formed by mixing 500. mL of 1.50 M HCN with 250. mL of 1.00 M NaOH. KaHCN = 6.2 x 10-10

  38. Total Points in course: 800 • Points to be decided next week: ~415

  39. Proposed Study Plan • Thursday: HE III Material (finish Lon Capa) • Friday: HE I Material • Saturday: HE II Material • Sunday: HE III Material • Monday: HE III Material • Tuesday: He III Material • Wednesday: HE I, II Material • Thursday: HE I, II, III Material

  40. A 100. mL solution of 0.10 M HF is titrated by 0.10 M NaOH. Calculate the pH when 0.0, 25.0, 50.0, 100.0, and 125.0 mL of NaOH have been added. KaHF= 7.4 x 10-4

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